Increased emphasis has been placed on the sterilization of medical instruments between uses on different patients. In dental offices for example, instruments are gathered after use, cleaned, packaged in sterilizable pouches, sealed in a closed volume defined by the pouch walls, and then subjected to a sterilizing environment such as an autoclave wherein steam or high temperature water vapor is used to sterilize process the instruments. Alternatively, the pouch-enclosed instruments are subjected to a sterilizing gas such as ethylene oxide. The instruments are then stored in the sealed pouches for later use. To ensure that a given pouch has been subjected to the sterilization procedures, indicators are used. These typically are printing inks having color change response to steam, high temperature water vapor or a sterilizing gas such as ethylene oxide, or other sterilizing agent, e.g. the ink permanently changes from gray to brown when exposed to sterilizing conditions.
Typical sterilizing pouches are formed of sheet materials printed with identifying brand names and other information on an outward face, and it has been the practice to place the indicator ink on this same face. This practice has several drawbacks, including lack of protection for the ink from frictional removal during handling and storage, and remoteness of the ink to the instruments being sterile processed, whereby the ink may record a sterilizing exposure but the instruments have not actually received the exposure, only the ink has.